A method and an arrangement for controlling a drive unit of a vehicle are disclosed, for example, in U.S. Pat. No. 5,692,472. In this patent, a quantity, which represents an output quantity of an internal combustion engine, is compared to a maximum permissible value pregiven for this quantity. This is done for monitoring purposes in the context of the control of the drive unit of a motor vehicle. Fault reaction measures are initiated when the quantity exceeds the pregiven permissible value. Examples for the output quantity of the drive unit are the power of the drive unit or a torque thereof, for example, the indicated torque, the output torque, but also the position of the throttle flap, et cetera. In one embodiment, the computer, which executes the control of the drive unit, includes at least two program levels separated from each other. The described comparison for monitoring purposes is computed in the second program level. The first program level is for programs which compute the functions provided for the control of the drive unit.
For determining the maximum permissible value, in general, and when no drive command of the operator is present, the largest occurring value of the output quantity is permitted in order to ensure an unlimited drivability. The output quantity can be adjusted by the idle control. Consumers such as a climate control compressor, a torque converter, et cetera operate greatly on the output quantity of the drive unit primarily for vehicles having small engines, low rolling resistance or low inner friction. Accordingly, relatively large permissible values are to be pregiven with the view to these consumers and the drivability in these applications.
The solution of the conflict between a monitoring as precise as possible (that is, in the case of a fault, the earliest possible response of the monitoring system) and the largest possible availability is primarily dependent upon the exact determination of the permissible value for the output quantity of the drive unit. This is especially the case when functions and/or components, which are driven by the drive unit, are provided whose activation changes the output quantity independently of the driver command, that is, especially when the output quantity must be increased. This is considered in the formation of the permissible value.
It is an object of the invention to provide a method and an arrangement for determining the maximum permissible value for the output quantity of a drive unit of a motor vehicle which solves the above-mentioned dichotomy satisfactorily.
The method of the invention for controlling a drive unit of a vehicle, the method including the steps of: forming a desired value for an output quantity of the drive unit at least on the basis of a driver command; controlling the drive unit to adjust the desired value; pregiving a maximum permissible value for the output quantity and reducing the output quantity when the output quantity exceeds the maximum permissible value; increasing the output quantity when at least one consumer or an ancillary function is activated independently of the driver command; increasing the maximum permissible value when the consumer or the ancillary function is actually switched on; and, deriving the actual switch-on on the basis of at least two quantities which represent the activation status of the consumer or ancillary function.
U.S. patent application Ser. No. 09/297,863, filed May 10, 1999, discloses inputting a maximum permissible value to which a desired value is to be limited when the output quantity exceeds the maximum permissible value. The desired value is for the output quantity of the drive unit of a motor vehicle. Here too, the above-described dichotomy occurs. Such a limiting function is, preferably, computed in the first program level.
U.S. Pat. No. 5,484,351 discloses to compute the requirement as to torque of a torque converter of an automatic transmission and of the compressor of a climate control system on the basis of operating variables. In a comparable manner, the requirement as to torque of other consumers such as of a power steering, of a generator, et cetera can be determined in dependence upon the quantities indicating the engine load. Furthermore, status signals are available which indicate the activation status of such consumers, for example, a force engagement in the transmission, an active climate control system, et cetera.
The redundant signals indicate the status of the at least one consumer and/or of the at least one function. With these redundant signals, the initially mentioned dichotomy is satisfactorily resolved. Especially the operational reliability as well as the availability of the control of the drive unit are adequately considered because the requirement of these components (consumer and/or function) on the output quantity is only then computed in the permissible value when the components are actually active. This leads to a more precise improved input of the permissible value for the output quantity of the drive unit.
It is a special advantage that the increase of the permissible value for an active component is only undertaken when an actually active component is recognized as being plausible based on the at least redundant status data as to the activity of the component. These status data are provided on various paths. If the at least two redundant pieces of data contradict each other, then the maximum permissible value for this malfunction is pregiven in the context of an emergency operation with the view to ensuring operational reliability of the drive unit control, as a rule, the maximum permissible value is pregiven to a lower value.
A special advantage is that consumers (such as a climate control compressor, a torque converter of an automatic transmission unit, a power steering unit, et cetera) as well as functions (such as a catalytic converter heating function), which increase the output quantity, are considered.